The majority of authors, myself included, depend on reviews to guide us away from the reefs of self indulgence and to give us some idea of who our audience is. We also need more than "I really liked or really hated your story". If it's good, why do you think so? On the other hand why, in your opinion, was it bad? Most authors if they are to survive develop thick skin or perhaps armor plating in certain cases. Constructive criticism, no matter how painful, is the gold standard for any reviewer worth his or her salt, and is highly prized by all authors genuinely interested in improving their craft. Naturally writing criticism is an art form too, and the only way you develop this talent is to write reviews, lots and lots of reviews. Don't worry, if you are off base either your fellow reviewers or the author (of course) will tip you to this fact and hopefully you can then regroup and write more reviews. I've worked both sides of the street and let me tell you, it's hard work, but when you do something good, be it a cogent review or a well written story it's worth all the trouble.